The invention relates to an electrodynamic actuator for optical storage systems comprising an electromechanical actuating device which is constructed to move an optical write and/or read unit into write and/or read operating positions relative to a storage medium, a radiation beam which is aimed at the operating positions by the optical unit being focussed at these positions by moving the optical system of the optical unit. The actuating device comprises a linear motor which comprises spaced-apart parallel stator sections, which are constituted by rod-shaped stator iron rods or elements carrying induction coils which are stationary relative to the stator. A permanent magnet is arranged between the stator sections and is guided to be longitudinally movable in a direction of translation between the axial ends of the stator sections. The permanent magnet carries the optical system of the optical unit and has a magnetic field which is oriented perpendicularly to the direction of translation and parallel to a central plane in which the stator irons, the induction coils and the permanent magnet itself are arranged.
Electrodynamic actuators of this type are known in audio, video and data technology. By means of an optical system a light beam is focussed onto a storage medium, for example a rotating disc (DE-OS 28 10 616). In this DE-OS the radiation beam is only used for reading; however, it can also be used for writing, as is known from DE-OS 16 13 987. Both during writing and reading the laser beam must first be brought to the write and/or read position by means of an electromechanical actuating device, after which the objective is focussed accurately at the point to be written or read.
A known electromechanical actuating device comprises a pivotal arm by means of which the radiation beam can be moved in a substantially radial direction over the disc surface. This positioning process is combined with an additional radial and tangential correction and with the focussing operation in a direction normal to the disc surface. In addition to single-stage radial positioning systems two-stage radial position systems are known in which a slide is initially coarse-positioned, after which fine-positioning is effected by means of a second stage. However, two positioning stages are intricate.
The prior-art electrodynamic actuator for optical storage systems thus performs movements in three directions, of which two directions are perpendicular to each other.
The known actuators are comparatively intricate. The optical system may be supported in a floating manner in a magnet system which is aligned via a coil system which is coupled to the optical system and which is disposed in the magnet field prior to this, however, the electromechanical actuating device already should have brought the optical unit in the operating position. An actuator which can perform a correction in a radial, axial and tangential direction is known, for example from DE-OS 35 29 091.
U.S. Pat. No. 46 13 962 describes an electrodynamic actuator for optical storage systems, in which an optical write/read unit is movable relative to a disc-shaped storage medium on a slide, which slide constitutes the movable part of a linear motor and for this purpose carries a permanent magnet. The stator of the linear motor comprises parallel rod-shaped stator iron elements carrying induction coils which are stationary relative to the stator. The slide with its permanent magnet is guided so as to be longitudinally movable between the axial ends of the stator sections and carries the optical unit. The permanent magnet is provided with polepieces, which direct the magnet flux out of a plane parallel to the central plane of the stator irons towards the central plane of the stator iron elements and the stator iron elements themselves. This magnet arrangement does not allow focussing movements of the optical unit.
From DE-PS 25 42 299 a linear motor is known whose rod-shaped stator iron elements carry a plurality of induction coils which are arranged after each other in the longitudinal direction and which can be switched into and out of circuit separately to shift the stator through a specific range, which results in a corresponding translation of the permanent magnet of the slide.
From EP 0,112,595 it is known to suspend the optical system of an electrodynamic actuator elastically by means of spring arms in order enable the focussing movements of the optical unit to be obtained. In this construction the coils of the linear motor are arranged on the slide and permanent magnets are arranged stationarily on the stator. The slide carries further coils, which surround the guide members of the slide and which provide the linear movement. All the coils of this system require flexible connections.